Crusader Kings II is a game about scheming, plotting and advanced nefariousness in a medieval setting. It has a cast of hundreds of characters with observable traits, from tactical geniuses to lackwit blunderers, via lustful philanderers and chaste holy men.

George R R Martin's Song of Ice and Fire books are about scheming, plotting and advanced nefariousness in a medieval setting. You can probably work out the rest. The two sync up so well, it only was a matter of time before Martin's low-fantasy setting was ported into Paradox's strategy game. Pleasingly, that time wasn't very long: the Game of Thrones mod was released in beta by a group of industrious CKII fans just eight months after the main game. It's now stable, comprehensive and easy to install. It's what I'll be using in this diary, and I heartily recommend you pop over to www.ck2agot.wordpress.com if you're interested.

A quick note: this series will contain spoilers for the Game of Thrones' TV series and books. I'll keep major revelations from the first book onwards under my helm, but if you've somehow managed to avoid the novels (first released in 1996, you layabout), and also the HBO series, then pick them up and gobble them down like a juicy capon leg before reading on.

Valar Morghulis. All men must die. I'm OK with that, but do all men have to die right now? There's a whole world to be seen, the continent of Westeros rendered in beautiful patchwork colours on Crusader Kings II's map screen. There's Dorne, jutting out into the sea in the south: sandy and warm, and split by culture – Dornishmen of sand, stone and salt. There's the greenery of the Reach and the Riverlands, filling the heart of the country. Highgarden's vineyards and Riverrun's, um, rivers, which one day I'd like to visit, be welcomed as a guest and a friend. To the west, Casterly Rock and Lannisport; to the east, the imposing crags of the Vale. I roll my mousewheel down and zoom in on the highest peak: the Eyrie, home of house Arryn. It's dusted white, like one of George's laboriously described cakes.

And then there's my (pretend) home: Winterfell. Westeros's north is big, more expansive but more empty than the continent's other regions. I'm expected to govern it alone, to manage a host of squabbling vassals and underlings, all while dealing with the seemingly inevitable: my own death.

I'm playing Crusader Kings II as Ned Stark, head of the Stark household, and boss of the north. The aGoT mod gives players a choice of starting period, and thus, their cast of characters. I chose to climb into Ned's armoured boots just after famous fatty – and Ned's best pal – Robert Baratheon has claimed the throne. It's supposed to be a time of peace after the loopy rule of mad King Aerys II, but George R R Martin doesn't make things easy for his characters

There's that morghulis thing, for one. Robert, after successfully rebelling against an incumbent king, loses a fight with a boar and unceremoniously dies in bed with his guts falling out. Ned doesn't even make it through one book before he has his head lopped off by his pal's son and kingly replacement: Joffrey Baratheon.

"Ned is naïve and unflinchingly honourable – to his own detriment."

In the books, Ned is naïve and unflinchingly honourable – to his own detriment. It's what gets him killed, and it's a trait I don't intend to take on myself. Crusader Kings II simulates all the intrigue of thousands of power-plays moving and interlocking across a vast political landscape. It lets you start plots against people, build spy networks, even kill your own wife. I'm not going to be like Ned. I'm going to scheme and sneak, backstab and betray. I'm going to take in the big picture, and play the pawns against each other.

One small problem: bar some minor dabbling, I've not played much of Crusader Kings. Its game mechanics are to me as courtly deceit and diplomacy were to Ned.

I must start small. Objective #1: not to die.

I spend the first year of Robert's reign jumpy. I'm not sure quite how much of aGoT's fiction is hardcoded into the mod, and I'm expecting Robert to die at any moment. If CKII had a letter-writing feature, I'd be sending him constant telegrams saying “FOR GOD'S SAKE STAY AWAY FROM PIGS” like a porcophobic weirdo.

I want to keep Robert on-side. He is, as king, the biggest presence in all Westeros. He's also got some seriously impressive claims. Claims are your ticket to more land in CKII: get a claim, and you can invade a territory without some higher power smiting you for your insolence. As Ned, I've got lordship of Winterfell – and therefore, the north – but nothing else. Robert has dibs on the southeastern Storm's End, as well as another four territories.

Fortunately, Robert likes me. Each CKII character – from king down to courtier – has two numbers on their character sheet. The first details how much they like you, the second how much you like them, dictated by a set of variables. Robert wishes Ned was a bit more hedonistic, knocking ten points off the score, but their shared bravery, battle history, and affinity for stabbing the shit out of things makes them fast friends. I could call Rob a fat bastard and he'd still share his capon with me.